Military officials said the new probe will closely examine Maj. Hasan's six years at the Walter Reed Army Medical Center, where he did his residency and worked as a psychiatrist before his July transfer to Fort Hood in Texas.
Army officials said the exact details of the new probe haven't been finalized, but said an announcement about the make-up of the investigative team and its exact powers would likely be made soon.
"The idea is to look at every aspect of Hasan's military career to see if the system could have done more to spot this guy," said one Army official familiar with the plan. "Everything's clear with hindsight, so the question is whether clues were missed along the way."
Three Army officials said the team would include uniformed members of the military and civilian experts from inside and outside government.
The officials said the team would have far-reaching investigative powers, but said it wasn't yet clear whether it would be able to issue subpoenas or otherwise compel testimony and the handover of documents.
The new probe will be separate from the continuing criminal probe into Maj. Hasan, who was charged with 13 counts of premeditated murder last week. Army officials say military prosecutors will seek the death penalty in the case, which isn't expected to get under way until sometime next year.
Lt. Col. Richard Spiegel, an Army spokesman, said he couldn't confirm that the military was preparing to launch an internal probe but said the service's top generals were determined to sort out precisely what happened in the run-up to the shootings.
"We're going to take a hard look at ourselves and the non-criminal aspects of this case," Col. Spiegel said. "We are still developing what that hard look is going to look like. As far as I know, it has not yet been finalized."
The Army investigators leading the criminal probe into the shootings with agents from the Federal Bureau of Investigation believe Maj. Hasan acted alone and received no financial or logistical support from foreign or domestic terror groups. But the investigators continue to examine the suspect's ties to overseas extremists as part of a broad look at whether his hardening religious beliefs may have motivated the attack.
U.S. intelligence agencies intercepted 10 to 20 communications over the past year between Maj. Hasan and radical imam Anwar al-Awlaki, who knew three of the Sept. 11 hijackers and hailed Maj. Hasan as a "hero" after the shootings. Investigators have also concluded that Maj. Hasan wrote an Internet posting defending suicide bombings, according to an official familiar with the probe.
The Army probe comes as Congress and the White House step up their own investigations into the shootings. President Barack Obama has ordered a government-wide probe into whether federal agencies, including the Pentagon and the U.S. intelligence community, properly shared the information collected about Maj. Hasan prior to the shootings. The relevant departments have been ordered to preserve all their records about Maj. Hasan until the probe is completed.
The Senate, meanwhile, has begun summoning senior Pentagon officials for questioning. On Thursday, its Homeland Security and Governmental Affairs Committee is scheduled to hold the first open hearing about the incident.